Pickup moving mechanism for optical disk apparatus and pickup moving method therefor

ABSTRACT

A pickup moving mechanism for making it difficult to generate a deviation between an optical axis of an optical pickup and a target position on a disk. This mechanism is constituted to comprise: an elevation member tilting a guide member based on an angle deviation of the optical axis of the optical pickup in a disk diameter direction, and inclining the optical pickup supported by the guide member in a direction in which the angle deviation of the optical axis decreases; a cam follower; a tilt motor; an eccentric cam; an urging means; and a controller for controlling a pickup motor operating a screw member and an engagement member so as to move the optical pickup in a direction in which the deviation of the optical axis in the disk diameter direction generated by inclination of the optical pickup decreases.

This application is a 371 of PCT/JP00/08318, filed Nov. 24, 2000.

TECHNICAL FIELD

The present invention relates to a pickup moving mechanism and a pickupmoving method for an optical disk apparatus for introducing a laser beaminto an optical disk to record or reproduce information. Moreparticularly, the present invention relates to a pickup moving mechanismand a pickup moving method for an optical disk apparatus having acontrol function, or a so-called tilt servo mechanism, for maintainingperpendicularity between the optical disk and an optical axis of anoptical pickup.

BACKGROUND ART

In an optical disk apparatus, it is essential that the angle between anoptical disk (hereinafter, referred to as disk) and the optical axis ofan optical pickup for introducing a laser beam to the disk and recordingor reproducing information is an angle at which the optical disk isperpendicular to the optical axis. In an actual apparatus, however, theabove-stated angle is deviated from the latter angle at which theoptical disk is perpendicular to the optical axis because of warpage ofthe disk, tolerance accumulation of a mechanism section or the like, amechanism for adjusting or controlling this angle is devised.

As an apparatus for adjusting the angle formed between the disk and theoptical axis of the optical pickup, there is known an apparatus shown inJapanese Unexamined Patent Publication No. 10-116479. The constitutionof the apparatus will be described based on FIG. 5.

A disk motor 2 rotating and supporting a disk (not shown) is fixed ontoa base 1, and an optical pickup 3 introducing a laser beam to the diskand recording or reproducing information is supported by a pair of guidemembers 4 and 5 so that the optical pickup 3 is movable in the diameterdirection of the disk. A pickup driving motor 6 for driving the opticalpickup 3 is fixed to the base 1 and the motor 6 transmits a drivingforce to a screw member 7 supported by bearings 1 a and 1 b provided onthe base 1 to be rotatable about a axial core through gears 8 and 9. Anengagement member 10 having an inclined portion 10 a engaged with thescrew member 7 and converting the rotation of the screw member 7 intothe movement of the optical pickup 3 is fixed to the optical pickup 3.One ends of the guide members 4 and 5 are supported by support portions11 and 12 and tiltable about the support portions 11 and 12,respectively. The other ends of the guide members 4 and 5 are in contactwith the tip ends of adjustment screws 14 and 15 which are engaged withthe female threaded portions of a beam member 13 fixed to the base 1 andwhich move in the direction of the optical axis 3 a of the opticalpickup 3 by their own rotation while being pressed by urging means,respectively.

With the above-stated constitution, if the angle of the optical axis 3 aof the optical pickup 3 with respect to the disk is deviated from theangle at which the optical axis 3 a is perpendicular to the disk due totolerance accumulation of the mechanism portion or the like, thedeviation is detected by a signal from the optical pickup 3 or a tiltdetection element, not shown. Due to this, by rotating the adjustmentscrews 14 and 15, the guide members 4 and 5 are tilted about the supportportions 11 and 12, respectively, in the direction of the optical axis 3a, the optical pickup 3 supported by the guide members 4 and 5 isinclined with respect to the base 1 and the deviation of the opticalaxis 3 a is adjusted. This angle adjusting device can be developed to anangle control device by driving the adjustment screws 14 and 15 using amotor.

As an optical disk apparatus utilizing angle control, there is known anapparatus shown in Japanese Unexamined Patent Publication No. 9-198687.The constitution of the apparatus will be described based on FIG. 6.

This optical disk apparatus is almost the same in constitution as thatshown in FIG. 5. Namely, a disk motor 2 rotating and supporting a disk16 is fixed on a base 1 and an optical pickup 3 introducing a laser beamto a disk 16 and recording or reproducing information is supported by apair of guide members 4 and 5 so that the optical pickup 3 is movable inthe diameter direction of the disk 16.

It is noted, however, a tilt detection element 17 for detecting theangle between the disk 16 and the optical axis 3 a of the optical pickup3 is provided on the optical pickup 3. Also,a pickup driving motor 6 fordriving the optical pickup 3 is fixed to the base 1, and driving gears18 and 19 engaged with the driving shaft of this pickup driving motor 6are rotatably supported. An engagement member 10 which is engaged withthis driving gear 19 and to which the driving force of the pickupdriving motor 6 is transmitted through the driving gears 18 and 19 isprovided to be fixed to the optical disk 3.

One ends of the guide members 4 and 5 are supported by support portions11 and 12, respectively, while the other ends of the guide members 4 and5 are supported by an elevation member 20 provided to be movable in adirection perpendicular to the base 1. The guide members 4 and 5 aretiltable about the support portions 11 and 12, respectively by theelevation member 20. The perpendicular movement of the elevation member20 is based on the engagement of cam followers 20 a formed on the bothsides of the elevation member 20 with eccentric cams 22 fixed to theoutput shaft of tilt motors 21 fixed to the base 1, respectively.

With the above-stated constitution, if the angle of the optical axis 3 aof the optical pickup 3 with respect to the disk 16 is deviated from anangle at which the optical axis 3 a is perpendicular to the disk 16, thedeviation is detected by a tilt detection element 17. Based on thedetected deviation, the tilt motors 21 rotate, the elevation member 20engaged with these tilt motors 21 through the eccentric cams 22 and thecam followers 20 a move in the perpendicular direction, respectively,whereby the guide members 4 and 5 tilt about the support portions 11 and12 in the direction of the axis 3 a, respectively. As a result, theoptical pickup 3 supported by the guide members 4 and 5 are inclinedwith respect to the base 1 and the deviation of the optical axis 3 a isadjusted.

However, if the angle adjusting device shown in Japanese UnexaminedPatent Publication No. 10-116479 is developed to an angle control devicefor driving adjustment screws by a motor, the following problems occur.If the optical pickup 3 is moved in the disk diameter direction, it isnecessary to exercise movement control while detecting the position ofthe optical pickup 3. To do so, detection means such as aphoto-interrupter is normally attached to either the pickup drivingmotor 6 or the screw member 7, or the pickup driving motor 6 is used asa stepper motor and the position of the optical pickup 3 is detectedusing the driving pulse of the motor 6, and the optical pickup 3 ismoved to a predetermined position based on a detection result. In thatcase, the optical axis 3 a of the optical pickup 3 thus moved does notsometimes agree with a target position on the disk to and from whichinformation is to be recorded or reproduced. If the axis 3 a does notagree with the target position, the optical characteristics of theoptical pickup 3 may possibly deteriorate or the optical pickup 3 may bepossibly required to be moved again, thereby disadvantageouslyincreasing access time. The problems stated above will be described withreference to FIG. 7.

FIG. 7 is a view showing the essential parts of the device describedwith reference to FIG. 5 seen from a different observation point. FIG.7(a) is a top view seen from the direction of the optical axis 3 a ofthe optical pickup 3 and FIG. 7(b) is a side view of FIG. 7(a) exceptfor the screw member 7. In FIG. 7(b), reference symbol 10 a denotes aninclined portion formed on the engagement member 10 and the engagementmember 10 is engaged with the screw member 7 on this inclined portion 10a. Since the screw member 7 is a right-hand screw, the inclined portion10 a is inclined by predetermined angle in a clockwise direction withreference to the optical axis 3 a.

The engagement portion between the screw member 7 and the engagementmember. 10 is typically shown in FIG. 7(c). In FIG. 7(c), the disk 16 isarranged in parallel to the base 1. The axial core 4 a of the guidemember 4 is, therefore, arranged in a direction along the base 1 and theoptical pickup 3 moves to a position away from the support portion 11 bya distance r1. Namely, in response to an instruction to move the opticalpickup 3 to the position away from the support portion 11 by thedistance r1, the screw member 7 moves the inclined portion 10 a engagedwith the inclined surface 7 a of the screw member 7 to the positionshown in FIG. 7(c) in the direction along the base 1. The optical axis 3a of the optical pickup 3 to which the inclined portion 10 a is fixed,extends perpendicularly to the base 1 and a position on the diskindicated by the intersection between the optical axis 3 a and the disk16 (hereinafter, referred to as disk diameter position) is located at aposition away from the support portion 11 by a distance r2 (=r1).

FIG. 7(d) shows a case where the disk 16 is inclined. In FIG. 7(d), thedisk 16 is inclined in a counterclockwise direction and the axial core 4a of the guide member 4 tilts downward toward the position shown in FIG.7(d) around the support portion 11 according to the inclination of thedisk 16. At this moment, a position detection signal obtained from thescrew member 7 or the pickup driving motor is the same as that in thecase of FIG. 7(c) described above. The inclined surface 7 a of the screwmember 7, therefore, moves to a position away from the support portion11 by the distance r1 as in the case of FIG. 7(c). On the other hand,the inclined portion 10 a engaged with the inclined surface 7 a of thescrew member 7 is slid downward and arranged at a position away from thesupport portion 11 by a distance r3 since the axial core 4 a of theguide member 4 is shifted downward by tilting. As a result, a differenceis generated between the position away from the support portion 11 bythe distance r3 and the position away from the support portion 11 by thedistance r1 on which the inclined portion 10 a and the optical axis 3 aare to be arranged. In addition, since the optical axis 3 a of theoptical pickup 3 to which the inclined portion 10 a is fixed is in thedirection perpendicular to the axial core 4 a of the guide member 4, anactual disk diameter position indicated by the intersection between theoptical axis 3 a and the disk 16 is located at a position away from thesupport portion 11 by a distance r4. As a result, the distance betweenthe position away from the support portion 11 by the distance r4 and thedistance away from the support portion 11 by the distance r1 furtherincreases.

As measures taken against the disagreement between the disk diameterposition on which the optical axis 3 a is to be arranged and the actualdisk diameter position as stated above, it is contrived to drive theoptical pickup 3 not by the screw member but by gears as in the case ofthe apparatus shown in Japanese Unexamined Patent Publication No.9-198687 stated above. This driving method can be assumed as a casewhere a surface denoted as the inclined surface 7 a in FIGS. 7(c) and7(d) is parallel to the optical axis 3 a. According to this drivingmethod, however, while the diameter position r3 shown in FIG. 7(d)agrees with the diameter position r1, the diameter position r4 stilldiffers from the diameter position r3. Furthermore, compared with thedriving method using the screw member, this driving method hasdisadvantages of an increase in the number of parts, the deteriorationof the positional accuracy of the optical pickup 3 due to backlash whichoccurs between the driving gears 18 and 19 shown in FIG. 6, theoccurrence of hysteresis and the like. Besides, since inertia isnormally high, this driving method has a disadvantage in that responsefrequency is low.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above-stated problemsand an object of the present invention is to provide a pickup movingmechanism for an optical disk apparatus using screw members as pickupdriving means, capable of making it difficult to generate a positionaldeviation between the optical axis of an optical pickup and a targetposition on a disk even if the optical pickup is inclined so as tomaintain perpendicularity between the disk and the optical pickup.

To obtain the above-stated object, the invention recited in claim 1 isan optical disk apparatus pickup moving mechanism comprising: a guidemember supporting an optical pickup introducing a laser beam to anoptical disk and recording or reproducing information, and guiding theoptical pickup to move in a disk diameter direction; pickup drivingmeans for driving the movement of the optical pickup; position detectionmeans for detecting a position of the optical pickup in the diskdiameter direction; tilt detection means for detecting an angledeviation of an optical axis of the optical pickup moved by a presetdistance with respect to a recording or reproducing target position onthe optical disk in the disk diameter direction; and tilt driving meansfor tilting the guide member in accordance with an output of the tiltdetection means, and for inclining the optical pickup supported by theguide member in a direction in which the angle deviation of the opticalaxis decreases, characterized by providing control means for controllingthe pickup driving means so as to move the optical pickup in a directionin which the deviation of the optical axis in the disk diameterdirection generated by inclination of the optical pickup decreases.

According to the above-stated constitution, while inclining the opticalpickup by the tilt driving means so as to control the angle between theoptical disk and the optical axis of the optical pickup, the deviationof the optical axis of the optical pickup in the disk diameter directiongenerated by the inclination can be decreased by moving the opticalpickup by the pickup driving means. It is, therefore, possible tointroduce a laser beam to a target position on the optical disk to orfrom which position information is recorded or reproduced.

The invention recited in claim 2 based on the constitution of claim 2 ischaracterized by constituting the pickup driving means to comprise: ascrew member provided along the guide member and rotating about an axialcore; an engagement member provided at the optical pickup, engaged withthe screw member, and converting rotation of the screw member intomovement of the optical pickup in the disk diameter direction; and arotation driving portion driving the rotation of the screw member.

The invention recited in claim 3 based on the constitution of claim 1 ischaracterized by constituting the tilt driving means to comprise: asupport portion tiltably supporting the guide member in a direction inwhich the guide member approaches and separates from a base; urgingmeans, provided between one end portion of the tiltable guide member andthe base, for urging the one end portion of the guide member in adirection in which the one end portion separates from the base; pressingmeans provided to face the one end portion of the guide member to beable to be freely elevated, and capable of pressing the one end portionof the guide member against an urging force of the urging means; andelevation driving means for driving elevation of the pressing means inaccordance with an output of the tilt detection means.

The invention recited in claim 4 based on the constitution of claim 2 ischaracterized by providing an inclined portion of the engagement memberengaged with a threaded groove of the screw member is provided so thatan angle of the inclined portion with the optical axis of the opticalpickup is greater than 0 and a tangent thereof is smaller than 2L/Rwhile information is recordable or reproducible up to a position of adiameter R on the optical disk and a distance between a support portionsupporting the other end portion of the guide member and the opticaldisk is L.

By setting the angle of the inclined portion to fall within theabove-stated range, it is possible to make the deviation of the opticalaxis of the optical pickup in the disk diameter direction derived fromthe inclination of the optical pickup smaller. The threaded groove ofthe screw member with which the inclined portion can be engaged isprovided.

The invention recited in claim 5 is characterized in that: when anoptical pickup introducing a laser beam to an optical disk and recordingor reproducing information is supported by a guide member and moved inan optical disk diameter direction, the optical pickup is moved alongthe guide member by a preset distance with respect to a recording orreproducing target position on the optical disk while detecting aposition of the optical pickup in the disk diameter direction; an angledeviation of the moved optical pickup from an optical axis in the diskdiameter direction is detected; the guide member is tilted based on adetection result, and the optical pickup supported by the guide memberis inclined in a direction in which the angle deviation of the opticalaxis decreases; and the optical pickup is moved in a direction in whichthe deviation of the optical axis in the disk diameter directiondecreases by inclination of the optical pickup.

According to the above-stated constitution, while inclining the opticalpickup so as to control the angle between the optical disk and theoptical axis of the optical pickup, the deviation of the optical axis ofthe optical pickup in the disk diameter direction generated by theinclination is decreased by moving the optical pickup. It is, therefore,possible to introduce a laser beam to a target position on the opticaldisk to and from which position information is recorded or reproduced.

The invention recited in claim 6 based on the constitution recited inclaim 5, is characterized in that when the optical pickup is inclined ina direction in which the optical pickup approaches the optical disk, theoptical pickup is moved toward an outer peripheral side of the opticaldisk in the disk diameter direction.

According to the optical disk apparatus pickup moving mechanism of thepresent invention, the tilt driving means for inclining the opticalpickup so that the optical disk is perpendicular to the optical axis ofthe optical pickup, and control means for controlling the pickup drivingmeans so as to move the optical pickup in the direction in which thedeviation of the optical axis generated by the inclination of theoptical pickup decreases are provided, whereby a laser beam can beintroduced to the target position of the optical disk to or from whichinformation is recorded or reproduced by decreasing the deviation.

As the pickup driving means, a screw member is provided along the guidemember, an engagement member engaged with the screw member is providedat the optical pickup and a rotation driving portion driving therotation of the screw member is provided, for example, whereby therotation of the screw member can be converted into the movement of theoptical pickup in the disk diameter direction. At this time, wheninformation up to a diameter R position on the optical disk can berecorded or reproduced and the distance between the support portionsupporting the other end of the guide member and the optical disk is L,the deviation of the optical axis of the optical pickup in the diameterdirection can be made smaller by providing the inclined portion of theengagement member engaged with the threaded groove of the screw memberso that the angle between the optical disk and the optical axis of theoptical pickup is greater than 0 and that a tangent thereof is smallerthan 2L/R.

Furthermore, according to the pickup moving method for an optical diskapparatus of the present invention, the optical pickup supported by theguide member is moved in the disk diameter direction, the angledeviation of the optical axis in the disk diameter direction isdetected, the guide member is tilted based on the detection result andthe optical pickup is inclined in the direction in which the angledeviation of the optical axis decreases, and the optical pickup is movedin the direction in which the deviation of the optical axis in the diskdiameter direction generated by the inclination decreases, whereby alaser beam can be introduced to the target position on the optical diskto and from which information is recorded or reproduced while decreasingthe deviation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing essential parts of an optical pickupmoving mechanism for an optical disk apparatus in a mode for carryingout the present invention;

FIG. 2 is a typical view for deriving a comparison reference value Δ′ ofa positional error of an optical pickup;

FIG. 3 is a typical view for deriving a comparison reference value Δ ofa positional error of a screw driven type optical pickup;

FIG. 4 is a correlation view showing inclinations of the positionalerror Δ;

FIG. 5 is a perspective view showing a configuration of essential partsof a conventional optical disk apparatus;

FIG. 6 is a top view showing essential parts of another conventionaloptical disk apparatus; and

FIG. 7 is a schematic view showing positional errors of an optical diskin the optical disk apparatus shown in FIG. 5.

MODES FOR CARRYING OUT THE INVENTION

A mode for carrying out the present invention will be described belowconcretely with reference to FIGS. 1 to 4.

FIG. 1(a) is a top view of essential parts of an optical disk apparatus,and FIG. 1(b) is a side view thereof. This optical disk apparatus isalmost the same in constitution as the conventional optical diskapparatus described above with reference to FIG. 5. The optical diskapparatus is constituted so that a disk motor 2 supporting and rotatinga disk 16 is fixed onto a generally rectangular base 1 and an opticalpickup 3 introducing a laser beam to the disk 16 and recording orreproducing information are provided. For description's sake, it isdefined that a coordinate system x is a direction along the surface ofthe base 1 and the width direction of the base 1, y is a longitudinaldirection, and z is a direction orthogonal to x and y. Symbol θindicates an angle in a y-z plane and a counterclockwise direction isdefined as +.

On the disk 16, information is recorded (or recordable) up to a maximumdiameter indicated by “R” and information is reproduced (or recorded) bya laser beam in a direction along the optical axis 3 a of the opticalpickup 3.

Guide holes 3 b and 3 c are formed on one side of the optical pickup 3,a guide hole 3 d. is formed on the other side opposite to the one side,and the optical pickup 3 is supported by a guide member 4 provided topenetrate the guide holes 3 b and 3 c and by a guide member 5 providedto penetrate the guide hole 3 d to be movable in a y direction.

A tilt detection element 17 for detecting the angle between the disk 16and the optical axis 3 a of the optical pickup 3 in the θ direction isformed on the upper surface of the pickup 3 facing the disk 16. Used asthe tilt detection element 17 is an element comprising, for example, onelight emission element emitting an infrared ray toward the disk 16 andtwo light receiving elements receiving a reflected light of the infraredray from the disk 16 so that an angle difference between the disk 16 andthe optical axis 3 a is detected based on a difference in light quantitybetween the reflected lights entering the two light receiving elements.

A pickup driving motor 6 for driving the optical pickup 3 in the ydirection is fixed onto the base 1 and connected to a screw member 7supported by bearings 1 a and 1 b provided on the base 1 to be rotatableabout an axial core so that the motor 6 can transmit power to the screwmember 7. Also, an engagement member 10 having an inclined portion 10 a,which has a predetermined angle β and which is engaged with the threadedgroove of the screw member 7, is fixed to the optical pickup 3, and therotation of the screw member 7 is converted into a movement of theoptical pickup 3 through the inclined portion 10 a. The pickup drivingmotor 6 is provided with position detection means 23 for detecting theposition of the optical pickup 3. Used as the position detection means23 is an element comprising, for example, an optical slit fixed to therotary shaft of the pickup driving motor 6 and a photo-interrupter fixedto a non-rotation portion so that a rotation quantity of the screwmember 7 is calculated based on the output therefrom to detect theposition of the optical pickup 3.

One end portions of the guide members 4 and 5 are held between supportportions 11 and 12 provided on the base 1 to restrict the movements ofthe guide members 4 and 5 in the x and z directions. The movementthereof in the x direction is restricted by guide restricting portions 1c and 1 d, and only the tilting thereof about the support portions 11and 12 in the θ direction can be made. At the positions of the supportportions 11 and 12, the guide members 4 and 5 are away from the disk 16by a distance “L” in the z direction. The other end portions of theguide members 4 and 5 are located below a flat elevation member 20supported by bearings 1 e and 1 f provided on the base 1 and movableonly in the z direction. The other end portions of the guide members 4and 5 are pressed in a +z direction by urging means 24 provided on theside of the base 1 in such a manner that they are always in contact withcontact convex portions 20 a and 20 b on the lower surface of theelevation member 20.

A tilt motor 21 for driving the elevation member 20 is fixed to the base1. An eccentric cam 22 is fixed to the rotary shaft of the tilt motor21. A cam follower 20 c is formed on the elevation member 20. Theeccentric cam 22 and the cam follower 20 c are kept in a state in whichthey contact with each other by pressing the elevation member 20 in the+z direction.

The function of the foregoing constitution will be described.

First, the movement of the optical pickup 3 will be described. In movingthe optical pickup 3 on the disk 16 to a predetermined radial positioncorresponding to a target position to or from which information isrecorded or reproduced, that is to say a position away from the centerof the disk by a predetermined distance, a driving signal is inputtedinto control means by input means, which is not shown, thereby drivingthe pickup driving motor 6 and rotating the screw member 7 connected tothis pickup driving motor 6. Whereby, the rotational force of the screwmember 7 is converted into a movement force in the y direction by theinclined portion 10 a engaged with the screw member 7, and the opticalpickup 3 to which the engagement member 10 having the inclined portion10 a is fixed is moved in the y direction. At this moment, therotational quantity of the screw member 7 is monitored by means of anoutput from the position detection means 23 and the screw member 7 isdriven to rotate until it is judged that the optical pickup 3 is locatedat the predetermined diameter position.

Next, description will be given to angular control between the opticalaxis 3 a of the optical pickup 3 and the disk 16. The tilt detectionelement 17 provided on the optical pickup 3 always detects the anglebetween the optical axis 3 a and the disk 16 in the θ direction. Whenthis angle is deviated from a normal value, that is to say, when theangle is deviated from an angle at which the optical axis 3 a isperpendicular to the disk 16, angular control is exercised.

If the disk 16 is warped in an umbrella shape or an upward convexmanner, the disk 16 has an angle in a +θ direction with respect to thebase 1 at the position of the optical axis 3 a shown in FIG. 1(b). Thisangle is detected by the tilt detection element 17 and the tilt motor 21is driven by the control means, not shown, in accordance with the outputof the tilt detection element 17. Then, as the tilt motor 21 rotates,the eccentric cam 22 presses the cum follower 20 c of the elevationmember 20 in a −z direction. Thereby, the elevation member 20 rotates ina −θ direction about the bearings 1 e and 1 f, the guide members 4 and 5move in a −z direction against the pressing force of the urging means 24by the contact concave portions 20 a, 20 b, and in result, the guidemeans 4 and 5 are tilted in the +θ direction about the support portions11 and 12, and the angle formed between the optical axis 3 a of theoptical pickup 3 inclined integrally with the guide members 4 and 5 andthe disk 16 becomes an angle at which the optical axis 3 a isperpendicular to the disk 16.

Conversely, if the disk 16 is warped in a cup shape or downward convexmanner and forms an angle in the −θ direction with respect to the base1, as the tilt motor 21 rotates, the elevation member 20 rotates in the+θ direction about the bearings 1 e and 1 f and the guide means 4 and 5are moved in the +z direction under the pressing force of the urgingmeans 23. As a result, the guide members 4 and 5 are tilted in the −θdirection about the support portions 11 and 12, and the angle formedbetween the optical axis 3 a of the optical pickup 3 inclined integrallywith the guide members 4 and 5 and the disk 16 becomes an angle at whichthe optical axis 3 a of the optical pickup 3 is perpendicular to thedisk 16.

In the foregoing operation, however, due to the inclination of theoptical pickup 3 which occurs integrally with the guide members 4 and 5,an error is generated between the position of the optical axis 3 a ofthe optical pickup 3 arranged based on the information of the positiondetection means 23 (which position will be referred to as the actualdiameter position of the optical pickup 3) and a predetermined diameterposition as in the case of the apparatus disclosed by JapaneseUnexamined Patent Publication No. 10-116479 stated above.

Due to this, the pickup driving motor 6 is driven by the control means,not shown, whereby the screw member 7 is rotated, the rotational forcethereof is converted into the movement force in the y direction by theinclined portion 10 a engaged with the screw member 7 and the opticalpickup 3 to which the engagement member 10 having the inclined portion10 a is fixed is moved in the y direction by a distance of the errorstated above.

Now, the quantity of the error between the actual diameter position ofthe optical pickup 3 and the predetermined diameter position is definedas Δ and derived from a formula. As a comparison reference, an errorbetween the actual diameter position of the optical pickup 3 in adriving system in which the screw member 7 is not used to drive theoptical pickup 3 and a predetermined diameter position is considered.This corresponds to the driving method using driving gears as shown inJapanese Unexamined Patent Publication No. 9-198687 stated above. Theerror at this moment is represented by Δ′ so as to differentiate fromthe error Δ in the above-stated apparatus.

FIG. 2 is a model view for deriving the error Δ′; FIG. 2(a) shows a casewhere the disk 16 and the guide member 4 (and 5) are parallel to thebase 1, and FIG. 2(b) shows a case where the disk 16 is inclined by anangle α in the θ direction and the guide member 4 (and 5) is alsoinclined by the angle a under angular control. To simplify the formulafor deriving the error, the positions of the support portions 11 and 12in they direction are set the same as the rotationally central axis ofthe disk motor 2. Reference symbol 4 a denotes the axial core of theguide member 4 and 2 a denotes the rotationally central axis of the diskmotor 2. The intersection between the axial core 4 a of the guide member4 and the optical axis 3 a of the optical pickup 3 is defined as apickup reference point P1 and the intersection between the optical axis3 a and the disk 16 is defined as a spot point P2. The distance betweenthe disk 16 and the axial core 4 a of the guide member 4 is L.

In FIG. 2(a), the pickup reference point P1 is located at the diameterposition indicated by a distance r1, the optical axis 3 a extends fromthe optical pickup 3 in parallel to the z axis and the spot point P2 islocated at the diameter position indicated by a distance r2. In thiscase, the distances r1 and r2 are equal and no error Δ′ occurs. Thediameter position indicated by a distance rn will also be referred to asa diameter position rn hereinafter.

Next, the state of FIG. 2(b) in which the disk 2 is inclined by theangle α from the state of FIG. 2(a) will be considered. Since theoptical pickup 3 is arranged based on information from the positiondetection means 23, the pickup reference point P1 is located at thediameter position indicated by the distance r1 as in the case of thestate of FIG. 2(a). However, since the guide member 4 (or axial core 4a) and the optical pickup 3 supported by the guide member 4 are inclinedby the angle α, the optical axis 3 a is inclined by the angle α in the θdirection with respect to the z axis. As a result, the spot point P2 islocated at the diameter position of the distance r4. The distancebetween r1 and r4 becomes the error Δ′. The distance L1 between the disk16 and the axial core 4 a of the guide member 4 is expressed by thefollowing mathematical formula 1 and the error Δ′ is expressed by thefollowing mathematical formula 2.

L 1=L·cos α.  Mathematical Formula 1

Δ′=L·cos α·sin α.  Mathematical Formula 2

Here, in considering the magnitude of the inclination a of the disk 16when the disk 16 is an ordinary 12 cm disk, it is expected that thecause of occurrence of α may be a warpage of the disc 16 alone,inclination of the disk motor 2, and inclinations due to toleranceaccumulations of the parts of a mechanism. The sum can be assumed to besmaller than one degree. If α is small, the approximation of thefollowing mathematical formula 3 is established. By assigning themathematical formula 3 to the mathematical formula 2, therefore, theerror Δ′ can be expressed by a mathematical formula 4. If specificnumeric values, e.g., L=10 mm and α=0.5 degree, are assigned, this errorΔ′ becomes 87 μm.

cos α≈1, sin α≈α, tan α≈α.  Mathematical Formula 3

Δ′≈L·α.  Mathematical Formula 4

Next, description will be given to how to derive the error Δwithreference to FIG. 3. FIG. 3 is a model view for deriving the error Δ;FIG. 3(a) shows a case where the disk 16 and the guide member 4 (and 5)are not parallel to the base 4, and FIG. 3(b) shows a case where thedisk 2 is inclined in the direction θ by an angle α and the guide member4 (and 5) are inclined by the angle α due to angular control. In FIG. 3,reference symbol 10 b denotes a virtual inclined portion which isparallel to the inclined portion 10 a formed on the engagement member 10and passes a pickup reference point 1 e. This virtual inclined portionis inclined in the direction θ with respect to the z axis by an angle β.The movement of the optical pickup 1 to the predetermined diameterposition r1 based on the information from the position detection means 9means the rotation of the screw member 7, and is considered to beequivalent to the movement of the virtual inclined portion 10 b toward aposition shown in FIG. 3(a).

In the state of FIG. 3(a), as in the case of FIG. 2(a), the pickupreference point P1 is located at the diameter position indicated by thedistance r1, the optical axis 3 a extends parallel to the z axis fromthe optical pickup 3 and a spot P2 is located at the diameter positionindicated by the distance r2. That is, the diameter position r1 is equalto the diameter position r2 at which the spot point 2 a is located andthe error Δ does not occur.

The state of FIG. 3(b) showing that the disk 16 is inclined by the angleα from the state of FIG. 3(a) will be considered. Since the opticalpickup 3 is arranged based on the information from the positiondetection means 23, the virtual inclined portion 10 b is located at aposition indicated by the distance r1 as in the case of FIG. 3(a).However, the pickup reference point is shifted from the position of (P1)in FIG. 3(a) to a position shown in FIG. 3(b). This implies, judgingfrom the actual apparatus, that even if the optical pickup 3 is locatedat the diameter position r1, the optical pickup 3 moves in the ydirection along the threaded groove of the screw member 7 in accordancewith the tilting of the guide member 4.

The diameter position r3 of the pickup reference point P1 in FIG. 3(b)will be obtained. The pickup reference point P1 is expressed by theintersection between the axial core 4 a of the guide member 4 and thevirtual inclined portion 10 b. If the support portion 11 is assumed asan origin O, the axial core 4 a of the guide member 4 can be expressedby the following mathematical formula 5 by approximating themathematical formula 3, and the virtual inclined portion 10 b can beexpressed by a mathematical formula 6. If z is set equal between the twoformulas, y and z to be obtained indicate the coordinates of the pickupreference point P1, and y at this moment becomes a diameter position r3.Accordingly, a mathematical formula 7 is obtained from the mathematicalformulas 5 and 6.

z=(−tan α)·y≈−α·y.  Mathematical Formula 5

Y=r 1+tan β·z.  Mathematical Formula 6

r 3=r 1/(1+α·tan β).  Mathematical Formula 7

Furthermore, the positional relationship between the pickup referencepoint P1 and the spot point P2 in FIG. 3(b) is equal to the positionalrelationship in FIG. 2(b). Accordingly, the difference between theradial positions r4 and r3 at the spot position P2 is equal to the errorΔ′ obtained while referring to FIG. 2(b) and (r4−r3) is obtained as thefollowing mathematical expression 8 using the mathematical expression 4.Further, the error Δ is defined by (r4−r1). Due to this, if themathematical formulas 7 and 8 are assigned to the definition formula ofthe error Δ and arranged in order, then the error Δ is expressed by amathematical formula 9. Besides, if the inclination α of the disk issmall and the angle β of the inclined portion 10 a of the engagementmember 10 is not so extremely large, e.g., α<one degree and β<45degrees, then a mathematical formula 10 is established. The mathematicalformula 9 can be approximated to a mathematical formula 11.

r 4−r 3=Δ′≈L·α.  Mathematical Formula 8

Δ=L·α−(α·tan β·r 1)/(1+α·tan β).  Mathematical Formula 9

α·tan β<<1.  Mathematical Formula 10

Δ=L·α−α·tan β·r 1=Δ′−α·tan β·r 1.  Mathematical Formula 11

This mathematical formula 11 will be described with reference to FIG. 4.FIG. 4 is a chart showing the correlation between the predetermineddiameter position r1 and the error Δ when the inclination α of the disk16 is a certain value (>0) A possible range of the diameter position r1is a range of the disk 16 in which information is recorded, or arecordable range, that is between r0 (minimum diameter) and R (maximumdiameter). Further, a line indicated by (β=0) is an error Δ derived ifthe screw member is not employed, which is a constant value Δ′ withoutdepending on r1.

If the angle β of the inclined portion 10 a falls within a certain rangeas shown in FIG. 4, the absolute value of the error Δ is always lowerthan the absolute value of the error Δ′ for a case where the screwmember 7 is not used. To be specific, β is in a range higher than 0 andlower than β0. β0 is defined as β if the error Δ is equal to −Δ′ whenthe diameter position r1 is the maximum diameter R and derived as avalue expressed by the following mathematical formula 12 based on themathematical formula 11.

tan β0=2 19 L/R.  Mathematical Formula 12

Accordingly, by selecting the inclination β of the inclined portion 10 aengaged with the screw member 7 to fall within an appropriate range or,to be specific, selecting the inclination β to fall within a rangehigher than 0 and lower than β0 shown in the mathematical formula 12 inthe +θ direction shown in FIG. 1(b), it is possible to make the error Δsmaller than the error caused to occur by the driving method using noscrew members 7.

What is claimed is:
 1. A pickup moving mechanism for an optical diskapparatus, comprising: a guide member supporting an optical pickup fordirecting a laser beam at an optical disk to record or reproduceinformation, and moving the optical pickup in a disk diameter direction;pickup driving means for moving said optical pickup; position detectingmeans for detecting a position of said optical pickup in a disk diameterdirection; tilt detection means for detecting an angle deviation betweenan ideal intersection point of an optical axis of with an optical diskwith no inclination of said optical pickup relative to the disk, and anactual intersection point of said optical axis for the optical pickupmoved by a preset distance with respect to a recording or reproducingtarget position on said optical disk in the disk diameter direction; andtilt driving means for tilting the guide member in accordance with anoutput of said tilt detection means, and for inclining the opticalpickup supported by the guide member in a direction in which the angledeviation of said optical axis decreases, wherein said pickup movingmechanism further comprises control means for controlling said pickupdriving means to move the optical pickup in a direction that causes adecreasing deviation between an ideal intersection point of the opticalaxis with an optical disk with no inclination of said optical pickuprelative to the disk, and an actual intersection point of said opticalaxis with the disk in the disk diameter direction, wherein saiddeviation is generated by inclination of said optical pickup anddecreases so that the deviation due to the inclination is canceled afterthe movement.
 2. The pickup moving mechanism for an optical diskapparatus according to claim 1, wherein the pickup driving meanscomprises: a screw member having a lengthwise axis and located adjacentthe guide member for rotating about the lengthwise axis; an engagementmember located at the optical pickup and engaging said screw member toconvert rotation of the screw member into linear movement of the opticalpickup in the disk diameter direction; and a rotation driving portionfor driving said screw member.
 3. The pickup moving mechanism for anoptical disk apparatus according to claim 1, further comprising a base,wherein the tilt driving means comprises: a support portion tiltablysupporting the guide member in a direction in which the guide memberapproaches and separates from the base; urging means located between oneend portion of the tiltable guide member and the base, and for urgingthe one end portion of the guide member in a direction separating theone end portion from the base; pressing means located for freelyelevatable movement while facing the one end portion of said guidemember, and adapted to press the one end portion of the guide memberagainst an urging force of said urging means; and elevation drivingmeans for driving the pressing means to elevate in accordance with anoutput of the tilt detection means.
 4. The pickup moving mechanism foran optical disk apparatus according to claim 2, wherein an inclinedportion of the engagement member engaging threaded groove of the screwmember is located so that an angle of the inclined portion with theoptical axis of the optical pickup is greater than zero and a tangentthereof is smaller than 2L/R when information is recordable orreproducible up to a position of a diameter R on the optical disk and Lis a distance between a support portion supporting another end portionof the guide member and the optical disk.
 5. A pickup moving method foran optical disk apparatus, comprising: directing a laser beam with anoptical pickup at an optical disk to record or reproduce information,wherein the optical pickup is supported by a guide member and moved inan optical disk diameter direction; moving the optical pickup along theguide member for a preset distance with respect to a recording orreproducing target position on an optical disk while detecting aposition of said optical pickup in the disk diameter direction;detecting an angle deviation of the moved optical pickup from an opticalaxis in the disk diameter direction; tilting said guide member based ona detection result, and inclining the optical pickup supported by theguide member in a direction in which the angle deviation of said opticalaxis decreases; and moving the optical pickup in a direction that causesa decreasing deviation between an ideal intersection point of theoptical axis with an optical disk with no inclination of said opticalpickup relative to the disk, and an actual intersection point with thedisk in the disk diameter direction, wherein said deviation is generatedby inclination of the optical pickup and decreases so that the deviationdue to the inclination is canceled after the increment.
 6. The pickupmoving method for an optical disk apparatus according to claim 5,further comprising, when the optical pickup is inclined in a directionin which the optical pickup approaches location of an optical disk,moving the optical pickup toward a location of an outer peripheral edgeof an optical disk in the disk diameter direction.